Tubular sheath for tension wires in prestressed concrete



Oct. 19, 1965 H. WITTFOHT 3,212,222

TUBULAR SHEATH FOR TENSION WIRES IN PRESTRESSED CONCRETE Filed July 29, 1963 BY a 9 fenf Ijent United States Patent 3,212,222 TUBULAR SHEATH FOR TENSION WIRES IN PRESTRESSED CONCRETE Hans Wittfoht, Cologne (Rhine), Germany, assignor to Metallschlauch-Fabrik Pforzheim, vorm. Hch. Witzenmanu G.m.b.H., Pforzheim, Germany Filed July 29, 1963, Ser. No. 302,757 Claims priority, application Germany, Aug. 16, 1958, M 29,063 3 Claims. (Cl. 52-230) This application is a continuation-in-part of my copending application Serial Number 832,267, filed August 7, 1959, now abandoned.

The present invention relates to improvements in tubular sheaths for use in prestressed concrete for encasing tension wires, rods or the like which extend through the concrete and are put under heavy tension to exert a pressure upon the concrete and thus effect the prestressing thereof after the concrete has set. Such tubular sheaths are embedded in the concrete when the same is being cast, and each of them is provided with a continuous corrugation in its wall extending helically around and along the sheath and having a part protruding inwardly and another part protruding outwardly of the sheath. While the outer surfaces of such a sheath engage and interlock with the concrete when set, the inside of the sheath is-filled with a cement emulsion or a grout which encases the tightened wires and fills out the helical corrugation from the inside so that, when the grout has set, the tension of the wires is taken up by the grout and the wall of the sheath and through the latter by the surrounding concrete.

YT he tubular sheaths used for this purpose prior to this invention were provided with inwardly and outwardly protruding corrugations which were either made of a substantially equal width or in which the inwardly protruding corrugations were made of a narrower width than the outer ones. It has now been found that such sheaths have certain disadvantages, namely that the engagement of the outer surfaces of the sheath with the surrounding concrete and the relative s'heering resistance between the sheath .and the concrete was rather poor, that the aggregates used in the concrete had to be of a very small size since otherwise the sheaths had to be spaced relatively far apart, that the compression or prestressing of the concrete was rather difiicult, that water or air pockets easily formed and remained in the grooves formed between the inwardly protruding corrugations or corrugation sections, that the tension wires had to engage under considerable pressure against the narrow inward corrugations of the sheath, that considerable time and effort was required for grouting the sheaths, and that if the tension wires were provided with transverse ribs or fins, these ribs easily passed into the grooves between the corrugations and engaged with the walls thereof and thus prevented the longitudinal displacement of the wires.

It is an object of the present invention to ascertain these disadvantages of the known sheaths and to determine the cause thereof, and to provide very simple and effective means for overcoming all of these dis-advantages without increasing the cost of production of the sheaths while maintaining all of the favorable features of the known sheaths.

Consequently, it is a further object of the invention to provide a tubular sheath of the type and for the purposes as described which may have the same general diameter as the known sheaths 'but still takes up less space within the concrete and which facilitates the application and filling in of the concrete mixture between the sheaths and permits the use of larger aggregates in the concrete mixture or a reduction of the distance between the in- 3,212,222 Patented Oct. 19, 1965 dividual sheaths as compared with the distance previously required.

A further object of the invention is to provide such a tubular sheath which has the advantage of requiring a smaller amount of injected cement emulsion or cement grout, and of permitting the grouting of the sheath to be carried out more speedily, and which reduces the danger of a formation of water or air pockets in the inner groove formed by the outwardly protruding corrugation of the sheath.

These and other advantages of the new sheath over those of the known constructions are attained generally by the simple procedure of making the inwardly protruding helical corrugation of the sheath of a greater width than the outwardly protruding corrugation so that these widths will have a ratio to each other of 1:1.2 to 1:4, further by making the inner corrugation, as seen in a cross section of the sheath taken longitudinallythereof, of a substantially trapezoidal shape; and by making the width of theinner corrugation relative to the inner diameter of the sheath of a ratio of 1:4 to 1:10; the inner diameter of the sheath relative to the outer diameter of a ratio of 121.05 to 1:125, and the outer diameter relative to the wall thickness of the sheath of a ratio of 1:0.01 to 1:0.004.

The greater width and the trapezoidal shape of the inner corrugation has the further advantage that the specific contact pressure of the tension wires against the inner corrugation will be reduced, that the danger that the tubular sheath might be damaged by such a pressure will be eliminated, and that the narrower inner helical groove forming the outer corrugation will be easily bridged so that transverse ribs or fins on the tension wires cannot hook into this groove and thereby prevent a displacement of these wires in the longitudinal direction.

When using tension wires with smooth outer surfaces it is advisable to provide the helical inner corrugation with an additional, inwardly protruding corrugation. This additional inner corrugation has been found to facilitate the grouting of the tubular sheath and to reduce the length of time required for the grouting operation. The additional inner corrugation is preferably made of a semicircular cross section and disposed centrally of the main inner corrugation.

These and other objects, features, and advantages of the present invention will become further apparent from the following detailed description thereof, particularly when read with reference to the accompanying drawings, in which- FIGURE 1 shows, partly in cross section, a side view of a tubular sheath according to the invention, in which the outer corrugation is made of a width in a ratio of about la -1.2 relative to the width of the inner corrugation;

FIGURE 2 shows a similar View of ,a sheath in which the outer corrugation has a width in a ratio of 1:3 relative to the width of the inner corrugation; while FIGURE 3 shows a similar View of a sheath according to a modification of the invention, in which the inner corrugation is provided with an additional inwardly protruding corrugation which forms a helical contact surface against which the outer tension wires within the sheath may engage.

The sheaths according to the invention, marked generally 1, 10, and 20 in FIGURES 1, 2 and 3, respectively, preferably consist of welded corrugated tubing. The corrugation on this tubing is of a helical shape and extends continuously along and around the tubing. It is formed of an inwardly protruding portion 2, 12, or 22, respectively, which is herein called the inner corrugation, and an outwardly protruding portion 3, 13, or 23, respectively, which is herein called the outer corrugation.

According to the most important feature of the invention, the inner corrugations 2, 12, or 22 is made of a greater width than the outer corrugation 3, 13, or 23. The individual sections of the inner corrugation are of a substantially trapezoidal shape and the entire inner corrugation thus winds like a helical ribbon in a direction co-axially to and around the longitudinal center of the sheath.

In FIGURE 1 of the drawings, the Width of the inner corrugation 2 is marked b the Width of the outer corrugation 3 is marked b the inner diameter of the sheath is marked d and the outer diameter is d,,, while the wall thickness of the sheath is marked S. All of these dimensions should preferably be in a certain relation to each other. The width b, of the wider inner corrugation and the width b of the narrower outer corrugation should be in a ratio to each other of at least 1212 to a ratio of approximately 1:4, the width b should be in a ratio of about 1:4 to 1:10 to the inner diameter (1,, this inner diameter d, should be in a ratio of about 111.05 to about 121.25 to the outer diameter d.,,, while the latter should be in a ratio of about 120.01 to about 110.004 to the Wall thickness S of the sheath.

While in FIGURE 1, the width of the inner corrugation 2 is only slightly larger than that of the outer corrugation 3, the sheath shown in FIGURE 2 has an inner corrugation 12 of a Width which is several times as large as the width of the outer corrugation 13. This embodiment according to FIGURE 2 is preferably applied for encasing tension wires or the like, not shown, which are provided with transverse ribs or fins. Due to the particular shape and relative sizes of the outer and inner corrugations, these transverse ribs will not hook into the helical groove between the adjacent sections of the inner corrugation so that the longitudinal movement of the tension wires will not be rest-rained. This embodiment according to FIGURE 2 has the further advantage that the specific radial contact pressure of the tension wires or the like against the inner surface of the sheath will be distributed over the greater surface of the inner corrugation so that the danger of damage to the sheath by such pressure will be practically eliminated.

If the tension wires or the like 25 have a smooth outer surface, as shown in FIGURE 3, it is advisable to provide the sheath 20 with a small additional helical corrugation 24 which protrudes inwardly at the center of the width of the inner corrugation 22 and is preferably of a semicircular cross-sectional shape. As clearly indicated in FIGURE 3, the outer tension wires 25 will then only have a substantial linear engagement with this smaller inner corrugation 24 and will not engage along the entire width of the inner surface of the inner corrugation 22. This embodiment has the advantage that the sheath 20 may be more easily and quickly grouted and the cement emulsion or grout will fil-l out the inner helical groove formed Within the outer corrugation 23, as well as the spaces adjacent to the small inner corrugation 24 completely so that no air or Water pockets will form therein.

The present invention has been found, in actual use, to have the following advantages over prior art reinforced tubular structures:

(1) Due to the fact that there is a larger engaging surface, the pressure of the tension wires and frictional nelationship will, at points where the tubular structure curves, be improved. In the case of oval corrugated tubes, the corrugations additionally make possible a ready bridging of the trough portion, While in the prior art tubing, the corrugations had to be lifted over the short crest portion.

(2) When the tubular structure is laid to follow a curved path, the bending of the tube occurs primarily in the short corrugations. In the case of prior art structures, this brought about a bending which, at certain points, reduced the inner diameter of the tube. This also .produced disadvantageous frictional effects. However,

in the tube according to the present invention, the short; corrugation lies on the outside so that deformations leave the inner diameter of the tube unchanged, despite the fact that some of the short outer corrugation may be beat; Consequently, the tube according to the present invention is better able to bend.

(3) With the same inner diameter of the tube, the pro-filing of the tube according to the present invention results in a reduction of the surfaces of the cutouts of the stressed cement cross section. This produces the following advantages:

(a) The stressed concrete cross section is not weakened as much.

(b) The concrete can be introduced more easily into the tube, because the larger outer diameter of the tube allows the use of coarser additives. Alternatively, with the use of a concrete of given workability, a smaller tube can be filled.

(c) The inner diameter of the tube can be smaller'.;

(d) Due to the fact that the internal volume defined by the inner corrugations is smaller, less filler is needed.- It is this factor which reduces the formation of water and air pockets as compared to tubes according to the prior art, which reduces the amount of grouting material that is required, and which accelerates the grouting time, which is especially important in the case of long tubes and during use in Warmer seasons.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments, but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, what I claim 1. A reinforced tubular structure, comprising, in combination: a corrugated tube having a helical inwardly protruding corrugation and a helical outwardly protruding corrugation between the adjacent sections of said inner corrugation, said inner corrugation having a greater width than said outer corrugation and said widths being of a ratio of from 1:12 to 1:4, said inner corrugation having in a longitudinal section of said tube a substantially trapezoidal shape and a width of a ratio of from 1:4 to 1:10 to the inner diameter of said tube, said inner diameter being of a ratio of from 1:1.05 to 1:1.25 to the outer diameter of said tube, and said outer diameter being of a ratio of from 1:0.01 to 120.004 to the Wall thickness of said tube; a plurality of tension elements located within said corrugated tube; and a cement emulsion located within the groove formed by the outer corrugation and encasing said tension wires.

2. A reinforced structure as defined in claim 1 wherein said tube is formed with an additional narrow helical corrugation protruding inwardly from the inner peripheral surface of said inner corrugation.

3. A reinforced structure as defined in claim 2 wherein said additional corrugation of said tube protrudes from said inner corrugation substantially centrally of the width thereof and is of a substantially semicircular shape.

References Cited by the Examiner UNITED STATES PATENTS 414,767 11/89 FOX 138l73 XR 1,057,505 4/13 Smith 138l73 XR 2,102,969 12/37 Patton l38--175 XR 2,677,957 5/54 Upson 50135.-

FOREIGN PATENTS 11,666 1887 Great Britain. 21,926 1892 Great Britain.

LEWIS J. LENNY, Primary Examiner.

EDWARD V. BENHAM, Examiner. 

1. A REINFORCED TUBULAR STRUCTURE, COMPRISING, IN COMBINATION: A CORRUGATED TUBE HAVING A HELICAL INWARDLY PROTRUDING CORRUGATION AND A HELICAL OUTWARD PROTRUDING CORRUGATION BETWEEN THE ADJACENT SECTIONS OF SAID INNER CORRUGATION, SAID INNER CORRUGATION HAVING A GREATER WIDTH THAN SAID OUTER CORRUGATION AND SAID WIDTHS BEING OF A RATIO OF FROM 1:12 TO 1:4, SAID INNER CORRUGATION HAVING IN A LONGITUDINAL SECTION OF SAID TUBE A SUBSTANTIALLY TRAPEZIODAL SHAPE AND A WIDTH OF A RATIO OF FROM 1:4 TO 1:10 TO THE INNER DIAMETER OF SAID TUBE, SAID INNER DIAMETER BEING OF A RATIO OF FROM 1:05 TO 1:1.25 TO THE OUTER DIAMETER OF SAID TUBE, AND SAID OUTER DIAMETER BEING OF A RATIO OF FROM 1:0.01 TO 1:0.004 TO THE WALL THICKNESS OF SAID TUBE; A PLURALITY OF TENSION ELEMENTS LOCATED WITHIN SAID CORRUGATED TUBE; AND A CEMENT EMULSION LOCATED WITHIN THE GROOVE FORMED BY THE OUTER CORRUGATION AND ENCASING SAID TENSION WIRES 